The present disclosure relates to a developing device incorporated in an image forming apparatus exploiting electrophotography, such as a copier, a printer, a facsimile machine, a multifunction peripheral thereof, etc., and to an image forming apparatus incorporating the developing device. More particularly, the present disclosure relates to a developing device which can be replenished with new two-component developer containing toner and carrier and meanwhile discharge surplus developer, and to an image forming apparatus incorporating such a developing device.
In an image forming apparatus, an electrostatic latent image formed on an image carrier comprising a photosensitive member or the like is made visible by being developed into a toner image by a developing device. Some such developing devices adopt a two-component developing system that uses two-component developer. In this type of developing device, two-component developer containing carrier and toner is stored in a developer container, there is provided a developer roller which feeds the developer to the image carrier, and there is provided a stirring member which transports, while stirring, the developer in the developer container to feed it to the developer roller.
In the developing device, toner is consumed in developing operation, whereas carrier is left unconsumed in the developing device. Thus, carrier stirred together with toner in the developer container deteriorates under mechanical stress as the carrier is stirred repeatedly, gradually diminishing the toner charging performance of the carrier.
As a solution, developing devices have been proposed that can replenish a toner container with new developer containing carrier and toner and that can meanwhile discharge surplus developer.
For example, a developing device is known in which two stirring members each composed of a rotary shaft and a helical blade formed in a helical shape on a circumferential surface of the rotary shaft are arranged parallel in transport chambers respectively. In the developing device, a partition portion is provided between the transport chambers, and in opposite end parts of the partition portion respectively, communication portions through which developer is delivered are provided. Moreover, a developer discharge port is formed on the downstream side of the transport chamber with respect to the developer transport direction. Between the stirring member and the developer discharge port, a reverse helical blade formed in a helical shape spiraling in the opposite direction to the helical blade of the stirring member is provided as a regulating portion integrally with the rotary shaft.
In this configuration, as new developer is supplied into the developer container, the developer is, while being stirred, transported to the downstream side of the transport chamber by rotation of the stirring members. As the reverse helical blade rotates in the same direction as the stirring member, by the reverse helical blade, a transport force is applied to the developer in the opposite direction to the developer transport direction by the stirring member. By the transport force in the opposite direction, the developer is blocked on the downstream side of the transport chamber, and increases its height; thus surplus developer moves over the reverse helical blade (regulating portion) to the developer discharge port and is discharged to the outside. In this way, it is possible to refresh the developer container with new developer while keeping the height of the developer in it.